Thousands more emails from the University of East Anglia, which was at the centre of the "climategate" row over global warming science two years ago, appear to have been posted online.

Hacked emails from the UEA’s Climatic Research Unit (CRU) were leaked online in 2009 before crunch UN talks in Copenhagen, which aimed – but ultimately failed – to secure a strong new global deal on tackling climate change.

Climate change sceptics claimed the emails showed scientists manipulating data to support a theory of man-made global warming, but a series of reviews later cleared researchers at the unit of any scientific impropriety.

However, the university was criticised for its failure to be sufficiently open and respond properly to freedom of information requests on its climate data.

The apparent new release of 5,000 emails from UEA comes in the run-up to the latest round of UN climate talks in Durban, South Africa, where it is hoped progress can be made towards agreeing a new deal to tackle emissions and maintaining the existing Kyoto climate treaty.

The release appears to show emails from a number of people including Prof Phil Jones, of CRU, and Prof Michael Mann of Penn State University in the US.

In a statement, the UEA said the email release appeared to be a “carefully timed attempt to reignite controversy” over climate science and cause maximum disruption at the upcoming climate talks, and that the quotes from them had been taken out of context.

The university said: “While we have had only a limited opportunity to look at this latest post of 5,000 emails, we have no evidence of a recent breach of our systems.

“If genuine, (the sheer volume of material makes it impossible to confirm at present that they are all genuine) these emails have the appearance of having been held back after the theft of data and emails in 2009 to be released at a time designed to cause maximum disruption to the imminent international climate talks.”